As a conventional vehicle periphery monitoring device, there is a known device that radiates spatial pattern light from a light projector, captures an image of an observed region irradiated with the pattern light by a camera, and measures a distance to an object present in the observed region on the basis of an irradiation direction of the pattern light in the captured image, an imaging direction of the pattern light, and the relative positional relationship between the light projector and the camera (see, e.g., Patent Reference 1).